1. Field of the Invention
The present invention relates to an anisotropic conductive film and the method for producing the film which is used for mounting a semiconductor chip on a substrate or connecting the substrates. More particularly, the present invention relates to the anisotropic conductive film comprising an electrically insulation member made from a porous metal oxide film made by anodic oxidation wherein the ability of electric connection of the film is raised.
2. Description of the Related Art
These days, in the technical field of mounting semiconductor chips such as LSI on a printed wiring board, there has been a demand for connecting chips in high density and reliably. Therefore, it is required that the anisotropic conductive film which is used for mounting the chips on the substrate satisfy the demand at a low cost. The film comprises an electrically insulation film and a conductive portion which is buried in the insulation film and comes electrically in touch with the semiconductor chip mounted on the substrate or an electrode pattern formed on the substrate. The film assembly is electrically conductive only in the direction along the film thickness, that is, in the direction perpendicular to the film surface.
Such an anisotropic conductive film is made in such a way that an electrically insulation sheet having a predetermined thickness is formed from, for example, resin material and that conductive particles made of, for example, metal are dispersed in the sheet or arranged at a predetermined interval. The insulation sheet is made from a resin which becomes adhesive when heated.
However, according to the film produced in the way as mentioned above, when the chips to be connected are arranged in high density, the conductive particles are also to be arranged in high density, which sometimes results in the short circuit between the adjacent particles.
Also, in accordance with the film in which the conductive particles are dispersed in the insulation sheet, the characteristic of conductivity is uncontrollable since the characteristic is dependent on the distribution of the particles.
Also, in accordance with the film in which the conductive particles are arranged in a predetermined interval, the particles are moved when the film is heated and pressed at the time of connecting operation, which disturbs the pitch of particles, thus resulting in the decrease of connection reliability.
Besides, the functional reliability of the film is also degraded when the film is heated or by moisture absorption.